Repeated administration of a drug often leads to an attenuation of the initial effects, and a dose of a greater magnitude is required order to obtain the original effect. This phenomenon is known as tolerance, and the current proposal is centered on identifying variables that contribute to this phenomenon. An influential view of how environmental factors contribute to the development of tolerance to effects on "purposive" behavior is the reinforcement-loss hypothesis. According to this view, tolerance develops when the initial effects of the drug lead to a loss of reinforcement. This is not a complete explanation, however, because the results of several studies have shown that tolerance can develop when there is no loss of reinforcement or, in some cases, increased reinforcement. The purpose of the proposed experiment is to investigate effects of cocaine-induced increases in reinforcement magnitude on the development of tolerance. A procedure that has been shown to increase reinforcement magnitude under an automaintenance procedure will be used.